424 NATURAL SCIENCE. t)EC.. 



enlarges within the protoconch into a rounded swelling, which is not 

 attached to the wall of the protoconch. In Nautilus the apex of the 

 conch is well known to be of a different nature." There is no rounded 

 protoconch attached to the end of the cone, but the outer wall of 

 the first loculus is marked by an elongate scar, the * cicatrix,' which 

 is at a little distance from the a.ctual apex and on the inner side of 

 the coil. Correlated with the absence of the globular protoconch, 

 there is always a passage left between the inner side of the first 

 loculus and the succeeding whorl of the shell. In other words, the 

 umbilicus is perforate ; whereas in the closely coiled ammonites this 

 space is entirely filled by the protoconch. Round the cicatrix the 

 shell is perceptibly thicker, and forms a raised margin to it. Within 

 the first loculus, the siphuncle is tubular and cylindrical, and is 

 attached to the wall of the conch almost, though not exactly, opposite 

 the spot where the cicatrix lies externally. 



When attention had once been directed to this distinction 

 between the protoconch-bearing shells of the Ammonoidea and of 

 the forms allied to Bdemnites and Spivula, on the one hand, and the 

 simple conchs of the Nautiloidea, on the other hand, it was supposed 

 by many eminent writers, such as Barrande and Branco, that an 

 insuperable distinction had been found between the Nautiloidea and 

 the Ammonoidea ; and Barrande especially, with his anti-evolutionist 

 opinions, was delighted to prove, as he thought, that the ammonites 

 could not possibly be derived from the nautiloids. So far was this 

 distinction pushed by some, and notably by that ingenious thinker 

 Munier-Chalmas, that the ammonites, goniatites, and their allies were 

 bodily transferred from their position with the Tetrabranchiata of 

 Owen's classification to the opposite division, namely the Dibran- 

 chiata.^ Others, of whom Waagen (i6), though with some hesitation, 

 was the first, have adopted the simpler and the safer course of doing 

 away with the classification of Owen, which, so far as it applied to 

 fossils, was based on characters of which we knew and for ever shall 

 know nothing, and of substituting therefor a division into three 

 Orders, based chiefly on the structure and relations of the shell. 

 These three orders are (i) the Nautiloidea, (ii) the Ammonoidea, (iii) 

 an order equivalent to the Dibranchiata of Owen, for which I have 

 proposed the name Coleoidea (i, 2), but for which others have 

 adopted the (as it seems to me) less appropriate and rather misleading 

 name of Belemnoidea (15, 4.) 



It would be going too far afield to consider the very remarkable 

 views as to the relations of the Octopoda that are held by Steinmann 

 (15), or the modifications of Steinmann's classification recently 

 proposed by Schwarz (13). The observations of Hyatt concern us 

 more closely. This suggestive writer maintained some time since 

 (11), on the evidence of specimens from St. Cassian preserved in the 



1 See for instance Bernard's " Elements de Paleontologie," reviewed in Natural 

 Science, vol. v., p. 298 ; October, 1894. 



